1. Field of the Invention
The present invention relates to a wired circuit board and, more particularly, to a wired circuit board used for a hard disc drive.
2. Description of the Prior Art
As shown in FIG. 4, the hard disk drive comprises a suspension board with circuit 52 on which a magnetic head 51 (See FIG. 5) is mounted, and a control circuit board 53, connected to the suspension board with circuit 52, for controlling the magnetic head 51.
As shown in FIG. 5, the suspension board with circuit 52 comprises an insulating base layer 55, a conductor layer 56 comprising a wired circuit pattern, and an insulating cover layer 57, which are sequentially laminated in layers on a metal board 54 of a stainless foil and the like.
The suspension board with circuit 52 is provided, at one lengthwise end portion thereof, with a magnetic head terminal portion 58 for mounting the magnetic head on it. The magnetic head terminal portion 58 is formed by opening the insulating cover layer 57 at one end portion thereof to expose the conductor layer 56 therefrom. Then, the magnetic head 51 is mounted on the one end portion of the insulating cover layer 57 and connected to the magnetic head terminal portion 58 through a plating layer 59.
The suspension board with circuit 52 is provided, at the other lengthwise end portion thereof, with a control circuit board terminal portion 60 for connection with the control circuit board 53. The control circuit board terminal portion 60 is formed by opening the insulating base layer 55 at the other end portion thereof to expose the conductor layer 56 therefrom. Then, the other end portion of the suspension board with circuit 52 is disposed opposite to one end portion of the control circuit board 53 and, then, the control circuit board terminal portion 60 is connected to a suspension board terminal portion 62 through a plating layer 61, as mentioned below.
The control circuit board 53 comprises an insulating base layer 63, a conductor layer 64 comprising a wired circuit pattern, and an insulating cover layer 65, which are sequentially laminated in layers. It also has stiffening layers 71, 72 laminated on the insulating base layer 63 at portions thereof corresponding to a preamplifier terminal portion 68 and an external terminal portion 66 on the side opposite to the side on which the insulating base layer 63 and the conductor layer 64 are laminated.
The control circuit board 53 is provided, at one lengthwise end portion thereof, with a suspension board terminal portion 62 for connection with the control circuit board terminal portion 60 as mentioned above. The suspension board terminal portion 62 is formed by opening an insulating cover layer 65 at one end portion thereof to expose a conductor layer 64 therefrom. Then, the other end portion of the suspension board with circuit 52 is disposed opposite to one end portion of the control circuit board 53 and, then, the control circuit board terminal portion 60 is connected to the suspension board terminal portion 62 through the plating layer 61.
The control circuit board 53 is provided, at the other lengthwise end portion thereof, with an external terminal portion 66 for connection with various control devices. The external terminal portion 66 is formed by opening the insulating cover layer 65 at the other end portion of the control circuit board 53 to expose the conductor layer 64 therefrom. Then, various control devices, not shown, are disposed opposite to the other end portion of the control circuit board 53 and then connected to the external terminal portion 66 through a plating layer 70.
The control circuit board 53 is provided with the preamplifier terminal portion 68 for connection with the preamplifier IC 67 at a location near the one lengthwise end thereof. The preamplifier IC portion 68 is formed by opening the insulating cover layer 65 at the location near the one end portion thereof to expose the conductor layer 64 therefrom. Then, the preamplifier IC 67 is mounted on the control circuit board 53 at the location near the one end portion of the control circuit board 53 and then connected to the preamplifier terminal portion 68 through a plating layer 69.
Electric signals output from the magnetic head 51 are transmitted therefrom to the control circuit board terminal portion 60 and the suspension board terminal portion 62 through the conductor layer 56 of the suspension board with circuit 52. Then, after having relayed via the control circuit board terminal portion 60 and the suspension board terminal portion 62, the signals are transmitted to the conductor layer 64 of the control circuit board 53 and amplified by the preamplifier IC 67. Then, the signals amplified are output from the external terminal portion 66 to the various control devices.
It is known that a relay flexible wiring circuit board is interposed between the suspension substrate and the control circuit substrate (Cf. JP Patent Laid-open (Unexamined) Patent Publication No. 2002-222578, for example).
Meanwhile, along with improvements in recent years to high-density of the wired circuit board, fine-pitch of wiring, and high-frequency of electrical signal, it is becoming important to control characteristic impedances in the transmission of the electrical signals from the suspension board with circuit to the control circuit board.
However, electrical resistance changes significantly at connection points between the control circuit board terminal portion 60 and the suspension board terminal portion 62, then causing inconsistency in characteristic impedance thereat.